1. Field of the Invention
The present invention relates to an organic light emitting display. More particularly, the present invention relates to an organic light emitting display capable of changing a display direction so as to permit a double-sided display.
2. Description of the Related Art
In general, an organic light emitting display electrically excites an organic phosphor to emit light by using voltage or current to drive M×M organic emitting cells arranged in an array to display images.
Since such an organic emitting cell has diode characteristics, it may be referred to as an organic light emitting diode (OLED). As shown in FIG. 1, the organic emitting cell may include an anode of indium tin oxide (ITO), an organic thin film, and a cathode layer. The organic thin film may have a multi-layer structure including an emitting layer (EML), an electron transport layer (ETL), and a hole transport layer (HTL) for maintaining balance between electrons and holes and for improving emitting efficiencies. The organic thin film may further include an electron injection layer (EIL) and a hole injecting layer (HIL). Additionally a metal cathode may be present.
FIG. 2 illustrates a partial perspective view schematically depicting an OLED capable of providing a double-sided display. The OLED may include a first transparent electrode 24, an emission layer 38, and a second transparent electrode 36, which are arranged between an upper transparent substrate 40 and a lower transparent substrate 22.
The first transparent electrode 24 may include an anode electrode formed on a lower glass substrate 22 by, e.g., vacuum-depositing or sputtering one of Indium-Tin-Oxide (ITO), Indium-Zinc-Oxide (IZO), or Indium-Tin-Zinc-Oxide (ITZO). The first transparent electrode 24 may used as a data electrode.
The emission layer 38 may include a hole injection layer 26, a hole transport layer 28, an organic emission layer 30, an electron transport layer 32, and an electron injection layer 34, which may be sequentially laminated on the first transparent electrode 24.
The second transparent electrode 36 may be a cathode electrode formed on the emission layer 38 by, e.g., vacuum-deposition or sputtering one of ITO, IZO, or ITZO.
The first transparent electrode 24 and the second transparent electrode 36 may have differently set work functions according to a composition ratio of an oxide and O2 plasma process. Accordingly, one of the work functions of the first transparent electrode 24 and the second transparent electrode 36 may be set lower than the other so that electrons and holes move. Owing to a difference between the work function of the first transparent electrode 24 and the work function of the second transparent electrode 36, the organic emission layer 38 may emit light using holes and electrons supplied from the first transparent electrode 24 and the second transparent electrode 36.
Visible light generated from the organic emission layer 30 may be discharged in both directions through the first and second transparent electrodes 24 and 36, and the upper and lower glass substrates 40 and 22. Accordingly, an electroluminescent (EL) device having a double-sided display function including the OLED may display an image in both front and rear directions.
FIG. 3 illustrates a schematic view of an organic light emitting display including the OLED shown in FIG. 2.
As shown in FIG. 3, the organic light emitting display may include an organic EL display panel 100, a scan driver 200, and a data driver 300.
The organic EL display panel 100 may include multiple data lines D1 to Dm, multiple scan lines S1 to Sn, and multiple pixel circuits 110. The data lines D1 to Dm may be arranged in a row direction, and the of scan lines S1 to Sn may be arranged in a column direction. The data lines D1 to Dm may transfer a data signal indicating an image signal to the pixel circuits 110. The scan lines S1 to Sn may transfer a selection signal to the pixel circuits 110. Each of the pixel circuits 100 may be formed at a pixel region, which may be defined by two adjacent data lines D1 to Dm and two adjacent scan lines S1 to Sn. Hereinafter, a pixel connected to a first scan line S1 is referred to as “P1”, and a pixel connected to an n-th scan line Sn is referred to as “Pn.”
The scan driver 200 may sequentially apply the selection signal to the scan lines S1 to Sn, respectively. The data driver 300 may apply a data voltage corresponding to the image signal to the data lines D1 to Dm.
The scan driver 200 and/or the data driver 300 may be electrically connected to the organic EL display panel 100. Further, the scan driver 200 and/or the data driver 300 may be coupled to the organic EL display panel 100 and may be mounted on a tape carrier package (TCP) in a form of a chip, which may be electrically connected thereto. Otherwise, the scan driver 200 and/or the data driver 300 may be coupled to the organic EL display panel 100 by mounting on a flexible printed circuit (FPC) or a film in a form of a chip, which may be electrically connected thereto. In contrast to this, the scan driver 200 and/or the data driver 300 may be directly mounted on a glass substrate. Also, the scan driver 200 and/or the data driver 300 may be substituted by a driving circuit or may be directly mounted on the driving circuit, which may be formed on the same layer as that of the scan lines S1 to Sn, the data lines D1 to Dm, and a thin film transistor.
On the other hand, in the organic EL display having a double-sided display function, the left and right of the front screen and the rear screen may reverse. Thus, in order to match a screen displayed on a rear surface of a display device with a front surface thereof, a first data signal may be applied to the first data line D1 in the front display and to the m-th data line Dm in the rear display. Further, an m-th data signal may be applied to the m-th data line in the front display and to the first data line D1 in the rear display.
Similar to a rotation of 180 degrees, besides the left and the right of a screen in the display panel, when a top and a bottom of the display panel reverse, as in the data driver, a scan driver may include a bi-directional shift register, which applies a data signal in a bi-directional manner. Namely, an emission display device in which a display screen rotates at 180 degrees may use a bi-directional scan driver to display the screens before and after rotation to thus be equally displayed. In this case, the bi-directional scan driver may apply a first selection signal to the first scan line S1 when the selection signal is sequentially applied from an upper side to a lower side (referred to as “forward scan” hereinafter), and to the n-th scan line Sn when the selection signal is sequentially applied from a lower side to an upper side (referred to as “reverse scan” hereinafter). Further, the bi-directional scan driver may apply an n-th selection signal to the n-th scan line Sn during the forward scan, and to the first scan line S1 during the reverse scan.
However, the pixel circuit may operate based on at least two different selection signals, e.g., an n-th selection signal applied to the current scan line Sn and an n−1-th selection signal applied to the previous scan line Sn−1. The aforementioned pixel circuit may have an arrangement structure, which may normally operate by applying the n-th selection signal to the n-th scan line Sn after an n−1-th selection signal was applied to an n−1-th scan line Sn−1 during the forward scan. In contrast, during the reverse scan, an applying direction of a scan line may be reversed. Accordingly, after the first selection signal was applied to the n-th scan line Sn, a second selection signal may be applied to the n−1-th scan line Sn−1, so that the pixel circuit may fail to normally operate.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.